Noise in Voltage Clamp

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Noise in Voltage Clamp

Post  mcs on Fri Jun 13, 2008 3:04 am

I'm using the robocyte to analyse compounds at LGIC. Resistance check (100-1000 kOhms), DC offest and impalement procede well. However when a switch to voltage clamp mode (-60 mV), I get a very noisy current trace (+/- 100 nA). This seems to be somewhat dependant on the position of the gilson liquid handler in relation to the roboocyte. Does anyone else experience this? Or is it an error in some parameters I have set. Any help would be appreciated. Cheers.

John

mcs

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Re: Noise in Voltage Clamp

Post  mcs on Fri Jun 13, 2008 3:04 am

Dear John

It's true that there can be some electrical interference of the Gilson. The proximity of the bath reservoir to any AC voltage source is critical in reducing noise - moving a power cable a few inches can make a lot of difference. Try to remove any voltage sources from the immediate vicinity of the reservoirs and tubing.

Sometimes a high noise level indicates that the amplifier parameters are not optimized. For example, a small noise introduced by minor oscillations of the perfusion can destabilize the amplifier, resulting in an increasing noise level until the amplifier oscillates and the clamp fails. This can be avoided by optimizing the amplifier settings as described in the manual. A very detailed description of the amplifier can be found in the Roboocyte Help of the latest software version (2.2.0.3). For a quick test, you can considerably lower the PI values, for example, P = 50 and I = 10 and see whether this makes any difference.

A third point that could be checked: New measuring heads sometimes show a high-frequency noise during the first minutes of recording because the perfusion tubing is hydrophobic. We are in the moment testing polyamide as a more hydrophilic perfusion tubing to solve this problem. A workaround can be to perfuse Ringer's in an empty well for a few minutes to hydrophilize the tubing before starting an experiment.

I hope this helps. Please inform us whether the problem could be solved.

Best regards, Christine
Roboocyte Product Manager

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Re: Noise in Voltage Clamp

Post  mcs on Fri Jun 13, 2008 3:05 am

Hi John,

you can also try to ground the needle of the gilson liquid handler:

Connect the needle with a grounded part of the roboocyte (e. g. one of the screws which holds the z-axis). At the gilson I use the screw which is used to fix the needle and the liquid level detector.

But I would expect, that it is Christines #3: the tubes. This will better with the next version of the measuring heads.

Ciao,

Mike

http://www.bayertechnology.com/ephys/

http://webkatalog.xantiva.de/ | http://blog.xantiva.de/ | http://flat.xantiva.de/ | http://singles.xantiva.de/

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Re: Noise in Voltage Clamp

Post  mcs on Fri Jun 13, 2008 3:05 am

Hi,
I have tried all of the suggestions and multiple recording heads, but nothing really seems to clear up the high frequency noise completely. It is definitely perfusion related, but not due to the gilson as the problem still exists with gravity perfusion. I have tried to optimize the vacuum of the system and this somewhat reduced the noise but not completely.

For now I have reduced the sampling rate to much lower and this eliminates the noise and is not that detremental to my recordings as they are not too fast. Regards

John

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Re: Noise in Voltage Clamp

Post  mcs on Fri Jun 13, 2008 3:05 am

Dear John

Could you send me a screen shot showing the problem to "support@multichannelsystems.com". Maybe we can come up with more suggestions.

Best regards, Christine

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